The present invention relates to an X-ray imaging apparatus having a projector-collimator installed within a movable diaphragm to project a light beam to an irradiation field position of X-ray on a subject.
In recent radiographing using an X-ray imaging apparatus, a light beam is radiated onto a subject to be radiographed. An operator checks the position of the light beam visually and thereby confirms and determines an X-ray irradiation position. In this way the operator is sure to radiate X-ray to a desired region on the subject while preventing the radiation of X-ray to an unnecessary region.
The projector-collimator for emitting the light beam is disposed in the interior of a movable diaphragm which restricts the irradiation field of X-ray. The projector-collimator changes the irradiation range of the light beam in interlock with the movable diaphragm changing an aperture to change the X-ray irradiation field (see, for example, Non-Patent Literature 1).
It is necessary that the X-ray irradiation field and the position of the light beam be coincident with each other accurately. The operator makes adjustment so that the irradiation position of the light beam becomes coincident with the X-ray irradiation field. On the other hand, the projector-collimator conducts a luminous flux emitted from a light source to the X-ray irradiation field through plural mirrors. At this time, the positions or inclinations of these mirrors are adjusted to adjust the position of the light beam on the subject.
[Non-Patent Literature 1] Tetsuo OKABE, et al., “Radiodiagnosis Device Engineering,” Ishiyaku Publishers, Inc., Oct. 1, 1997, pp. 336-338
According to the above background art, however, the adjustment of the light beam position on the subject is difficult to perform and is inferior in point of accuracy. More particularly, the position of the light beam on the subject which beam is guided through plural mirrors is changed in interlock with movement of those mirrors. However, the change in position of the light beam is correlated with all of the mirrors and therefore it is necessary to adjust the plural mirrors simultaneously.
Particularly, in the case where the light beam radiated from the projector-collimator is a frame line which clearly shows a frame of the irradiation field of X-ray, it is necessary that strain or the like of the light beam be also taken into account. This is a cause of making the adjustment of light beam more difficult.